A device for the electric heating and cooling of a fluid medium, in synthetic resin processing machines and especially injection-molding machines, and particularly in association with the mold-filling sleeve of the nozzle thereof, is known.
This sleeve or nozzle generally comprises an axially extending passage upon which radial passages communicate with the respective parts of the mold. The device includes an electric heater and at least one coolant tube in a common carrier or jacket extending around the bushing. The jacket is composed of a highly thermally conductive material and the heater and cooling tube are embedded therein with the cooling tube being located somewhat more closely to the synthetic resin flow passage than the electric heater.
A device of this type is described, for example, in German Patent No. 23 47 987. The jacket comprises form-fitting parts surrounding the cylinder through which the synthetic resin material is displaced, i.e. jacket segments, whose inner curvature corresponds to the outer curvature of the cylinder against which the segments are seated.
This device can be applied to the cylinder of an injection-molding machine so that, during the processing of the thermoplastic material, any overheating which can result from friction heat during the working of the plastic material can be prevented by the cooling fluid and any lack of heating be made up by the electric heater.
This device, however, is relatively complex and expensive, at least in part as a result of its two-part construction.
Indeed, the fabrication of the device is expensive and may result in unreliable units because of the difficulty in holding the electric and cooling tube parts in appropriate relative positions during the production of the jacket segments.
Because of the fabrication methods used, i.e. casting of the bed of the jacket segments around the previously positioned tube and heater, relatively large wall thicknesses must be provided and hence, upside in those regions in which the injection-molding machines may experience the greatest coil heat development in the synthetic resin material, a thermal inertia because of such large wall thicknesses may preclude satisfactory cooling. Consequently, where the danger of overheating is the greatest, the units may be least responsive because, at least in part, of the gaps between the two units and the regions which must be traversed by bolts or the like to clamp the segments onto the cylinder.